Balanced armature electro acoustic transducers have long been fundamental components of communications equipment ranging from telephones to hearing aids. In essence, this type of speaker uses an armature positioned in an area of magnetic flux created by opposite poles of a magnet. An alternating current typically is passed through a coil positioned around the armature. This induces a fluctuating magnetic flux in the armature to change the magnetic polarity of a portion of the armature positioned between opposite poles of a magnet. The polarity of the armature depends on the direction of the AC current running through the coil, and the armature is attracted to one or the other of the magnetic poles of the magnet in an alternating sequence. This causes the armature to vibrate, and the vibrating movement of the armature is then used, either directly or indirectly, to move air and to thereby create sound waves.
A limitation to the performance of conventional balanced armature electro acoustic devices, whether used as speakers or microphones, is that their characteristic frequency spectra deviate from being perfectly flat, spectral flatness being one representation of a lack of distortion, a very desirable characteristic for acoustic (and most other) transducers. This spectral deviation or “signature” arises from the fundamental structural properties that are characteristic of all conventional balanced armature devices: the mass and springiness of the armature itself, the sound producing diaphragm and its chamber(s), and, in most conventional speaker of this type, the connector element and its attachments that link the armature and the diaphragm. Numerous techniques have been developed to minimize the disadvantages of this inherent signature, including, for example, the use of so-called “ferro-fluids” for damping the system and improving the transducer's dynamic performance.
Notwithstanding the substantial enhancements to these general types of transducers, room remains for improving and simplifying the frequency signature, minimizing the frictional and other mechanical losses, and improving the efficiency of this type of speakers. In many applications, it also is desirable to further reduce the size of the transducer. For example, when used in a hearing aid or earphone application, it is desirable to have a transducer that is small enough to comfortably fit within a human auditory canal. Similarly, when used as a component of a device such as a cell phone, the small size of the transducer allows the size of the device to be minimized.